The search masks used to define search panels have three sections – the search controls, the display columns, and refiners. All three use managed properties as their source.
Managed properties must be scoped (defined) at the Farm level as MacroView Search does not support site collection scoped managed properties.
Make sure the managed properties are searchable, queryable, retrievable, and (refinable if needed)
Managed properties for Controls
Managed properties for controls should return results correctly when used in a Search Centre (or in the search box on a site) with the KQL syntax “managedproperty:text”.
“Type” is not so important provided they return results correctly.
The exception here is date columns which must be of type date and mapped to the appropriate date crawled property (qDate) control to use the Date picker control.
In SharePoint Online it is not possible to define the Type of your own managed property. Instead, SharePoint makes a range of predefined "Refinable" managed properties available, eg RefineableDate01 which you can give an "Alias" to, and map to the desired managed property. The "Refineable" properties include string, etc
Managed properties for Result Display and Refining
The display and refinable columns need to be user friendly. A mapping to the simple crawled property ows_column will usually suffice. This prevents more complex columns like user, managed metadata, or content type, etc, from displaying a lot of unnecessary and confusing text